1. Field of the Invention
The present invention relates to an apparatus and method of molding a heat-resistant container particularly from a synthetic resin such as polyethylene terephthalate (which will be called xe2x80x9cPETxe2x80x9d).
2. Description of the Prior Art
In general, a synthetic resin thin-walled packaging container known as biaxial stretching blow molded container is formed by positioning an injection-molded or extruded preform having an appropriate temperature for stretching within a mold and stretching the preform in its longitudinal direction corresponding to the longitudinal axis of the container while at the same time expanding the same preform in its lateral direction under the action of a pressurized gas blown into the mold.
Depending on selection of a material used to form the container, however, a problem was raised in that the container deformed when it was filled with a hot content such as a thermally sterilized fruit juice beverage.
To overcome such a problem, a proposal such as the applicant""s Japanese Patent Application Laid-Open No. 3-205124 has been made in which the blow molding step to be executed after the temperature of the preform has been regulated is divided into primary and secondary sub-steps. In the primary blow molding sub-step, a primary molding is formed in the desired form of a container. The primary molding is thermally processed to shrink and then subjected to the secondary blow molding sub-step to form the final container.
Such a proposed molding process can provide a heat-resistant container which is improved in mechanical strength through the thermal treatment before the secondary blow molding sub-step.
More particularly, the thermal treatment before the secondary sub-step removes a strain produced at the primary blow molding sub-step or a residual stress due to stretching, and crystallizes the oriented walls to a higher level. This improves the heat resistance of the final product which may be placed under a severe temperature condition in markets.
To attain such a heat-resistant container, it is required that the temperature of the primary molding has been increased sufficiently to improve the crystallinity in the primary molding at its oriented walls.
However, the prior art could not smoothly increase the temperature of the molding since the necessary heat was only transmitted to the molding through radiation within an atmosphere.
Therefore, a long time is required until the temperature of the molding reaches a level that can provide the necessary crystallinity for the molding to have its sufficient heat resisting property. Thus, time for heating or conveying the molding must be prolonged. This may extend the molding cycle or increase the dimensions of the container molding apparatus including the heating conveyor path.
It is therefore an object of the present invention to provide an inexpensive and compact apparatus and method of molding a heat-resistant container to be filled with a hot content such as a thermally sterilized fruit juice, which can increase the crystallinity of the container and also reduce the residual stress thereof in a reliable and short manner, resulting in improvement of the form stability at high temperature to avoid a thermal deformation.
Another object of the present invention is to provide a heat-resistant container molding apparatus and method of molding a heat-resistant container in an efficient blow molding manner without thermal loss.
Still another object of the present invention is to provide a heat-resistant container molding apparatus and method of molding a heat-resistant container, in which when a plurality of steps using clamping mechanisms are used, it can be prevented to increase the installation space due to a stroke required to open and close the respective mold.
A further object of the present invention is to provide a heat-resistant container molding apparatus and method of molding a heat-resistant container, in which a preform can be sufficiently cooled such that the blow molding step will not be influenced by the heat history of an injection molded preform.
To accomplish these objects, the present invention provides a heat-resistant container molding apparatus comprising:
a primary molding section for blow-molding preforms into primary moldings by using a primary blow mold having split molds;
a heat treatment section for heat treating the primary moldings to obtain intermediate moldings by bringing the primary moldings into contact with inner walls of a heat treatment mold having split molds while pressurizing an interior of each of the primary moldings within the heat treatment mold; and
a final molding section for blow-molding the heat treated intermediate moldings into final products within a heated final blow mold having split molds.
According to the present invention, the heat transfer is carried out by heating the primary molding in direct contact with the inner wall of the heat treatment mold while pressurizing the interior of the primary molding. Therefore, the temperature of the molding can efficiently be increased for a short time. At the same time, the apparatus can be compacted. In addition, the residual stress produced in the primary molding can reliably be removed for a short time to increase the crystallinity of the primary molding. As a result, the form stability can be improved at a raised temperature reliably to prevent a container from being thermally deformed when the container is filled with a hot content such as a thermally sterilized fruit juice beverage or the like.
Since the heat shrinkage and thus uneven wall thickness is prevented by pressurizing the interior of the primary molding within the heat treatment mold, an uneven wall thickness and irregular heat resistance can reliably be prevented at the final blow molding step. Thus, a desired heat can certainly be provided to the molding without variability. This can stabilize the shrinkage in the intermediate molding after being heat-treated. Consequently, the wall-thickness distribution of the final product can also be stabilized.
In the final molding section after the heat treating step, a strain in the final product can be removed by heat treating it within the final heated blow mold when the intermediate molding is blow-molded into the final product in the final heated blow mold. Thus, the heat stability can be improved to increase the heat resistance in the final product.
In the apparatus of the present invention, it is preferred that it comprises a receiving section for receiving the preforms to be primarily molded and a removing section for removing the final products and wherein the primary molding, heat treatment and final molding sections being located adjacent to one another.
Since the primary molding, heat treatment and final molding sections are sequentially positioned, the final blow molding step can be carried out immediately after the heat treating step while maintaining the heat in the heat treated molding. Thus, the blow molding step can efficiently be performed without heat loss.
It is also preferable that the apparatus of the present invention further comprises conveyor means for intermittently conveying a given number of preforms to be simultaneously molded to the primary molding section and a given number of moldings to be simultaneously molded to the heat treatment and final molding sections respectively, and wherein each of the primary molding, heat treatment and final molding sections includes a mold clamping mechanism for clamping the split molds, the primary molding, heat treatment and final molding sections are rectilinearly disposed in a transfer direction.
Such mold clamping mechanisms require a stroke of opening and closing the split molds and thus an increased installation space. If the mold clamping mechanisms are disposed opposed to one another, the spacing between the adjacent conveyor means will unnecessarily be increased. This will also increase the installation space.
When the primary molding, heat treatment and final molding sections respectively having the mold clamping mechanisms are rectilinearly disposed in the direction of conveyance as in the present invention, the strokes of opening and closing the split molds can rectilinearly be taken in the same direction. Since the strokes of opening and closing the split molds in the mold clamping mechanisms are avoided from overlapping in the opposed direction, the installation space can be minimized. By executing the heat treatment using the heat treatment molds, further, the heat treatment can efficiently be carried out for a short time.
In such a case, it is preferable that the split molds of the heat treatment mold in the heat treatment section have cavity configuration substantially equal to that of the primary blow mold in the primary molding section and a mechanism for heating the heat treatment mold to a heat treatment temperature.
Since the primary moldings are brought into contact with and heated by the heat treatment molds which have been heated to the necessary heat treatment temperature by the heating mechanism, the temperature of the primary moldings can efficiently be raised for a short time. Further, the residual stress produced at the primary molding section can certainly be removed for a short time to provide an improved crystallinity. As a result, the form stability at a raised temperature can be improved certainly to avoid a container from being thermally deformed when it is filled with a high temperature content.
It is further preferable that the conveyor means forms a substantially rectangular conveyor path and the primary molding, heat treatment and final molding sections are disposed on a long side of the rectangular conveyor path.
In such an arrangement, the spacing between the long opposite sides of the conveyor path can be minimized to reduce the entire installation space.
It is further preferable that the receiving section is disposed on a short side of the conveyor path.
By disposing the primary molding, heat treatment and final molding sections requiring the mold opening/closing spaces on the one longer side of the conveyor path as described, a given spacing between the longer opposed sides of the conveyor path can be provided. If the receiving and removing sections are disposed on one shorter side of the conveyor path, the distance between the longer opposed sides of the conveyor path can be reduced.
It is preferable in this case that the receiving section is used as a removing section for removing final products.
The heating and heat treating sections need relatively longer time, while the receiving and removing steps in the receiving and removing sections do not relatively consume time. Therefore, such a single receiving/removing section can contribute to reduce the installation space.
It is further preferable that a plurality of heating units for heating preforms are disposed between the receiving section and the primary molding section.
Thus, the preform heating time can be sufficiently secured such that the preforms will certainly be heated to the blow molding temperature.
It is further preferable that the present invention includes a plurality of heating units for heating preforms received at the receiving section and wherein the plurality of heating units are disposed on at least one side of the conveyor path excluding the long side on which the primary molding, heat treatment and final molding sections are disposed.
Thus, the conveyor path of a conveyor having no mold clamping mechanism can effectively be used to secure an appropriate heating distance and thus a sufficient heating time.
In such a case, it is preferable that each of the heating units has a rotary mechanism for rotating the preforms.
The heating unit can uniformly heat the preform around the circumference thereof while being rotated by the rotary mechanism. This can avoid any uneven wall thickness in the product during the blow molding step.
It is further preferred that the conveyor means includes carrier members for conveying moldings to be simultaneously molded upside down and a conveyor chain mounted on the carrier members and engaged with sprockets which are disposed in the conveyor path at corners thereof, each of the carrier members having a rotating sprocket engaged with preform rotating means in each of the heating units.
In such an arrangement, the moldings are supported upside down on the respective carrier members and conveyed to the respective molding sections by the conveyor chain engaging the sprockets. At the same time, the carrier members and thus associated moldings are rotated about their own axes by the rotating sprockets engaging the preform rotating means at the respective heating units. Thus, the moldings can be heated uniformly around their circumferential direction to avoid any uneven wall thickness during the blow molding step.
In another aspect, it provides a heat-resistant container molding apparatus for molding a heat-resistant container, comprising:
a preform molding section for injection-molding preforms;
a heat-resistant container molding section for blowmolding the preforms into heat-resistant containers; and
a conveyor line for conveying the preforms to the heat-resistant container molding section after removing the preforms from the preform molding section, the conveyor line including cooling means located at least at an upstream side for cooling the preforms.
According to this aspect, the preform removed from the preform molding section is conveyed to the heat-resistant container molding section through the conveyor line. In the heat-resistant container molding section, the preform is blow-molded into a heat-resistant container. During transfer through the conveyor line, the preform is forcedly cooled at least at the upstream side by the cooling means. This can avoid a sticking between adjacent preforms during transfer and also sufficiently cool the preforms through a short transfer distance.
It is preferable that the conveyor line includes preform rotating and conveying means for conveying the preforms while rotating them.
Thus, the preforms can be cooled uniformly around their circumference by rotating them through the preform rotating and conveying means while conveying in the conveyor line.
It is preferable that the preform rotating and conveying means includes upstream intermittent conveying means for intermittently conveying preforms to be simultaneously molded and downstream continuous conveying means for continuously conveying the preforms from the upstream intermittent conveying means.
Thus, the simultaneously injection-molded preforms from the upstream intermittent conveying means can be conveyed while maintaining a pitch between adjacent preforms during the injection molding step or preventing a sticking therebetween. The downstream continuous conveying means can convey the preforms in close contact with one another. This can avoid any excess transfer while securing sufficient preforms.
It is also preferable that the conveyor line provides a transfer distance and time which allow preforms to be cooled to a temperature sufficiently lower than a blow-molding temperature.
Thus, the blow molding step will not be influenced by the heat history of the injection-molded preforms. According to the present invention, further, the conveyor line can more compactly be formed by conveying the preforms, unlike the prior art machines wherein the primary moldings are conveyed.
The present invention further provides a method of molding a heat-resistant container, comprising:
a primary molding step for blow-molding injection molded preforms into primary moldings in a primary blow mold;
a heat treating step for heat treating the primary moldings to obtain intermediate heat treated moldings by bringing the primary moldings into contact with an inner wall of a heat treatment mold while pressurizing an interior of each of the primary moldings within the heat treatment mold; and
a final molding step for blow-molding the intermediate heat treated moldings into final products in a final blow mold.
According to the present invention, any residual stress produced in the primary molding step can certainly be removed to provide an improved crystallinity by heat treating the primary molding obtained by the primary blow molding step within the heat treatment mold at the heat treating step. As a result, the form stability can be improved at a raised temperature reliably to avoid any thermal deformation in a container when it is filled with a hot content.
It is preferable that the method of the present invention also comprises the steps of:
receiving preforms prior to the primary molding step; and
removing final products after the final molding step.
It is also preferable that a plurality of preform heating steps are carried out between the receiving step and the primary molding step.
Each of the plurality of preform heating steps includes the step of rotating the preforms while heating them.
It is further preferred in the present invention that a primary molding has a height slightly larger than that of a final product and a diameter slightly smaller than that of the final product barrel, thereby providing a margin compensating the heat shrinkage when the primary molding is thermally treated. In such a case, it is preferable that the intermediate molding after heat treated is formed into a size slightly smaller than that of the final product and has a sufficient wall-thickness distribution in its height direction. Thus, the intermediate molding will not be pinched in its diametrical direction by the final blow mold when it is closed. By providing the intermediate molding having its size slightly larger than that of the final product, thus, the intermediate molding will not be stretched in the final blow molding step. Therefore, only a few strain can be produced in the final blow molding step. Additionally, the strain thus produced can substantially completely be removed by heating the final blow mold. As a result, the heat stability can be improved in the final product.
If the heat treatment step is so designed that the intermediate molding has its size substantially equal to or slightly smaller than that of the final product, depending on the heat treatment temperature and time, the intermediate molding can be controlled at the heat treatment step such that it has a size substantially equal to or slightly smaller than that of the final product.
Where a primary molding has its cylindrical barrel having substantially no tongued and grooved face, the barrel may have no axial undercut and be formed with a circumferentially integral pot-shaped part corresponding to the cylindrical barrel of the heat treatment mold. Thus, only the shoulder of the primary molding can be formed through a split mold, resulting in minimization of the other expensive split mold sections. Furthermore, this permits a large-sized mold clamping mechanism to be omitted, thereby reducing the manufacturing cost of the entire system and its installation area.
If the heating temperature at the final blow mold is equal to or higher than a desired heat-resisting temperature, the heat stability at that heat-resisting temperature can be improved to avoid any deformation in a container thereat.
It is further preferable that the primary molding has a diameter larger than that of the final product and a height about 10% larger than that of the final product. Thus, the intermediate molding can be formed such that it will have a size substantially equal to or slightly smaller than that of the final product through the shrinkage after the heat treatment of the primary molding. This prevents the molding from being pinched by the final blow mold.
If the heat treatment time in the heat treating step is set between five seconds and ten seconds, the size of the intermediate molding can be stabilized while shortening the molding cycle. More particularly, if the heat treatment time is less than five seconds, the shrinkage in the intermediate molding will be unstable to scatter the size of the intermediate molding. If the heat treatment time exceeds ten seconds, the molding cycle becomes too long. It is thus preferable that the heat treatment time is in the range of five to ten seconds.
If the blow molding time in the final molding step is set between five seconds and fifteen seconds, a practical heat-set effect can be provided to minimize the molding cycle.
According to a further aspect, the present invention provides a method of molding a heat-resistant container, comprising:
a preform molding step for injection-molding preforms;
a conveying step for removing the injection molded preforms from the preform molding step and conveying the preforms to a conveyor line; and
a heat-resistant container molding step for receiving and heating the preforms conveyed by the conveyor line and subsequently blow-molding the preforms into heat-resistant containers, the conveying step including a cooling step located at least at an upstream side of the conveyor line for cooling the preforms.
In such an arrangement, the conveying step preferably includes the step of rotating the preforms while conveying them.
In a further aspect, the present invention provides a heat-resistant container molding apparatus for molding a heat-resistant container, comprising:
a receiving section for receiving primary moldings obtained by blow-molding preforms;
a heat treatment section for bringing the primary moldings received by the receiving section into contact with an inner wall of a heat treatment mold and for heat treating the primary moldings while pressurizing an interior of each of the primary moldings within the heat treatment mold, whereby intermediate moldings are obtained;
a final molding section for blow-molding the intermediate heat-treated moldings into final products in a heated final blow mold;
a removing section for removing the final products; and
conveyor means for conveying the moldings to the receiving, heat treatment, final molding and removing sections.
According to this aspect, the apparatus is defined by the primary molding receiving section, the heat treatment section, the final molding section and the removing section which are separated from one another. This enables the injection-molding and primary blow molding devices to be omitted from the apparatus of the present invention, resulting in a compacted system. If an existing blow-molding machine is used as a primary molding device, a heat-resistant container molding system can simply be formed only by connecting the apparatus of the present invention to that blow molding machine.
It is preferred in the present invention that receiving and removing unit replaced with the receiving and removing sections, heat treatment section and final molding section are disposed at three points which are equidistant from a center point and wherein the conveyor means comprises split type neck support members for grasping necks of the moldings, a neck support fixing plate formed by a split plate for holding and allowing the neck support members to be open and closed, and a rotary plate for supporting the neck support fixing plate at positions corresponding to the receiving and removing unit, heat treatment section and final molding section and for rotatably conveying the neck support fixing plate to positions corresponding to the receiving and removing unit, heat treatment section and final molding section.
Thus, the molding can be moved to the receiving and removing unit, heat treatment section and final molding section merely by intermittently rotating the rotary plate through 120 degrees. This can simplify the conveying means. If the receiving and removing unit, heat treatment section and final molding section are disposed within the rotating locus of the rotary plate, the respective sections can efficiently be disposed to improve the installation space.
It is further preferably that the conveying means has a rectilinear conveyor path and the heat treatment section is located adjacent to the final molding section on the rectilinear conveyor path.
Thus, the primary molding is heat treated and finally blow molded along the rectilinear conveyor path. The final blow molding step can be carried out immediately after the heat treatment step while maintaining the heat treat. The blow molding step can efficiently be performed without heat loss.
In a further aspect, the present invention provides a method of molding a heat-resistant container, comprising:
a receiving step for receiving primary moldings obtained by blow-molding preforms;
a heat treating step for bringing the primary moldings received by the receiving step into contact with an inner wall of a heat treatment mold and for heat treating the primary moldings while pressurizing an interior of each of the primary moldings within the heat treatment mold, whereby intermediate moldings are obtained;
a final molding step for blow-molding the intermediate heat-treated moldings into final products in a heated final blow mold; and
a removing step for removing the final products.